If it's only 3.5 lbs it must truly be a baby still. How old exactly is it? It probably is just so young that it can't hold it yet.I have a Lhasa Apso, which I understand is very similar to a Shih Tzu. My Lhasa liked to go in closets, other crates, etc. He doesn't like to go outside so would rather find a secret place inside to go. He is never allowed out of my sight in the house unless crated.